1. Field of the Invention
The present invention relates to a movable structure having a movable body allowed to move with respect to a support, and more particularly to a movable structure manufactured by a micromachine manufacturing process or the like.
2. Description of the Related Art
In a micromachine element, a movable structure having a movable body supported by a pair of springs is often used. FIG. 22 shows this movable structure. As shown in FIG. 22, the movable structure 700 comprises a movable body 712, supports 716, and springs each of which connects the movable body 712 and the support 716. The movable body 712 is allowed to move with respect to the supports 716 by deformation of the springs 714.
In this movable structure 700, the movable body 712 is supported by a pair of springs which extend therefrom. Therefore, the springs 714 must be at least partially deformed. That is, a part or all of each spring 714 must be deformed. Deformation of the spring 714 generates the locally excessive stress therein at times. Generation of the excessive stress lowers the drive efficiency of the micromachine element or increases the non-linearity of the drive characteristic of the micromachine element.
Generation of the excessive stress can be avoided by lowering Young's modulus of the spring 714, e.g., slenderizing and thinning the spring 714. However, such a slender and thin spring disadvantageously considerably lowers the impact resistance of the micromachine element.
In order to avoid generation of the excessive stress in the spring while maintaining the impact resistance of the micromachine element, there is known the movable structure using a flexuous structure spring. FIG. 23 shows a deflection mirror element using such a movable structure. As shown in FIG. 23, the deflection mirror element 800 comprises a movable structure and a substrate 832 supporting the movable structure. The movable structure comprises an inner movable plate 812 having a reflection surface, an outer movable plate 816 surrounding the inner movable plate 812, a pair of flexuous structure springs 814 connecting the inner movable plate 812 and the outer movable plate 816, a pair of supports 820 positioned outside the outer movable plate 816, and a pair of flexuous structure springs 818 connecting the outer movable plate 816 and the support 820.
The supports 820 are fixed to the substrate 832, and the substrate 832 has a pair of inner drive electrodes 834 opposed to the inner movable plate 812 and a pair of outer drive electrodes 836 opposed to the outer movable plate 816.
In this deflection mirror element, when an appropriate potential difference is given between the inner movable plate 812 and each drive electrode 834, the electrostatic attraction is generated therebetween. The inner movable plate 812 is turned about an axis L1 by this electrostatic attraction. Further, the outer movable plate 816 is turned about an axis L2 together with the inner movable plate 812 by the electrostatic attraction which is generated between the outer movable plate 816 and each drive electrode 836 by giving an appropriate potential difference therebetween. As a result, the direction of the inner movable plate 812 can be arbitrarily adjusted.
Rotation of the movable plate 812 gives the tensile force to the flexuous structure springs 814 and 818 along axes thereof. With respect to this tensile force, the flexuous structure springs 814 and 818 demonstrate flexural deformation. Therefore, the stress generated inside the flexuous structure springs 814 and 818 is reduced. In other words, the flexuous structure springs 814 and 818 ease the stress generated therein. This realizes improvement in the drive efficiency or reduction in the non-linearity of the drive characteristic.
In the micromachine element (deflection mirror element) having such a flexuous structure springs, however, when an impact shock is given to the micromachine element, abnormal deformation may be possibly generated in the flexuous structure springs. For example, as shown in FIG. 24, a part of the flexuous structure spring 850 may be possibly attached and can not be removed (sticking may occurs). Alternatively, as shown in FIG. 25, the flexuous structure spring 850 may move onto the support 852 corresponding to the support or the movable body and can not return to the original position.